Note: Descriptions are shown in the official language in which they were submitted.
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SEISMIC SOURCE AND METHOD OF GENERATING A SEISMIC WAVE IN A
FORMATION
The present invention relates to a seismic source, in
particular a down-hole seismic source, comprising an actuator.
The present invention further relates to a method of generating
a seismic wave in a formation.
A down-hole seismic source is described in US
patent 4,702,343. This down-hole seismic source is provided
with a vibrator body in the form of a clamping plate which is
brought into contact with an inside wall of a subterranean bore
hole by means of radially directed pistons. The pistons are
operated by means of a hydraulic fluid. In order to excite a
seismic wave, the clamping force exerted by the pistons can be
varied in a pulsating mode by operating a servo control valve
that actuates the pistons. The servo control valve is
controlled by a signal and power from surface passing through
an electric line, for generation of which signal an electric
oscillator is required.
It is an object of some embodiments of the invention
to obviate the need of an electric oscillator.
In accordance with the invention, there is provided a
seismic source comprising an actuator having a rotary part and
a reciprocative part, conversion means to convert a rotation of
the rotary part into a reciprocal movement of the reciprocative
part, and a vibrator body that is connected to the
reciprocative part of the actuator by means of a spring.
The oscillatory source is based on mechanical
rotation, for which the rotary means can be located down
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hole a subterranean bore hole. Since oscillation is
generated by rotation, there is no need of an electric
oscillator.
In use, the vibrator body can be brought in contact
with an earth formation. The spring serves as a resilient
means to accommodate the amplitude of the reciprocative
part to avoid damage to the seismic source and/or the
earth formation.
Frequency control of the reciprocating motion is
achieved by controlling the rotary speed of the rotary
part, which can be controlled by a relatively slowly
varying signal compared to the oscillation frequency.
The reciprocative motion can be a linear
reciprocative motion. The conversion of rotation into
reciprocative motion preferably includes frequency
coupling between the reciprocative part and the rotary
part.
Advantageously, the conversion means comprises
mechanical interaction means arranged to mechanically
convert the rotation of the rotary part into the
reciprocal movement of the reciprocative part. Because of
the mechanical conversion, the reciprocative part can be
driven by a high force, and thus a high power can be
transmitted to the reciprocating motion of the
reciprocative part. The achievable power is at least
higher than in the case of valved pulsating of the piston
pressure as in the prior art described in US patent
4,702,343.
In the context of this specification the spring can
be any kind of elastic body, but in an advantageous
embodiment the spring is a liquid spring. Such a liquid
spring may comprise a pressure chamber filled with a
liquid, whereby relative movement of the reciprocative
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part with respect to the vibrator body causes compression or
decompression of the liquid. Herewith, a suitable stiff spring
is provided. Moreover, a liquid spring has as an advantage
that its pressure can be changed in order to adjust a biasing
force.
A drive means, in particular a hydraulic motor, can
be arranged to drive the rotation of the seismic source rotary
part.
The invention also provides a method of generating a
seismic wave in a formation, wherein an actuator is driven,
whereby driving the actuator comprises driving a rotary part
into rotary movement and converting the rotary movement into
reciprocative movement of a reciprocative part, and
transferring energy of the reciprocative movement into the
formation via a spring.
According to another aspect of the present invention,
there is provided a seismic source comprising an actuator
having a rotary part and a reciprocative part, conversion means
to convert a rotation of the rotary part into a reciprocal
movement of the reciprocative part, and a vibrator body that is
connected to the reciprocative part of the actuator by means of
a spring, wherein the conversion means comprises mechanical
interaction means arranged to mechanically convert the rotation
of the rotary part to the reciprocal movement of the
reciprocative part, and wherein the mechanical interaction
means comprises first and second corrugated coupling surfaces
provided on the rotary part and the reciprocative part, which
first and second coupling surfaces are slidably arranged with
respect to each other.
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According to another aspect of the present invention,
there is provided a seismic source comprising an actuator
having a rotary part and a reciprocative part, conversion means
to convert a rotation of the rotary part into a reciprocal
movement of the reciprocative part, a vibrator body that is
connected to the reciprocative part of the actuator by means of
a spring, and adjustment means for varying the stiffness of the
spring, wherein the adjustment means is controllable in
response to a reciprocation frequency of the reciprocative
part.
According to still another aspect of the present
invention, there is provided a method of generating a seismic
wave in a formation, wherein an actuator is driven, whereby
driving the actuator comprises driving a rotary part into
rotary movement and using mechanical interaction to convert the
rotary movement into reciprocative movement of a reciprocative
part, and transferring energy of the reciprocating movement
into the formation via a spring, wherein the mechanical
interaction comprising first and second corrugated coupling
surfaces provided on the rotary part and the reciprocative
part, which first and second surfaces are slidably arranged
with respect to each other.
The invention will be described hereinafter in more
detail and by way of example, and more embodiments will be
described hereinafter, with reference to the accompanying
drawings in which:
Fig. 1 is a schematic cross section of a down-hole
seismic source according to one embodiment of the invention;
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Fig. 2 is a schematic view of a bearing support for
use in the seismic source of Fig. 1;
Fig. 3 is a schematic view of an actuator for the
seismic source of Fig. 1;
Fig. 4 depicts a schematic cross section of a
down-hole seismic source according to another embodiment of the
invention and installed in a drill collar;
Fig. 5 depicts a schematic cross section of a
down-hole seismic source according to still another embodiment
of the invention and installed in a drill collar;
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Fig. 6 is a schematic overview of a hydraulic motor
arrangement for driving the seismic source;
Fig. 7 is a schematic diagram of the hydraulic motor
arrangement adopted inside a drill collar;
Fig. 8 is a schematic overview of the hydraulic
motor arrangement according to another embodiment;
Fig. 9 is a schematic overview of a drill collar
provided with the hydraulic motor arrangement; and
Fig. 10 is a schematic cross section of an expel
reservoir for the embodiment of Fig. 9.
In the drawings, like reference numerals refer to
like parts.
Fig. 1 shows in schematic cross section an
embodiment of a seismic source in contact with a
subterranean formation 103. An actuator is provided,
having a rotary part 104 and a reciprocative part 105,
and a vibrator body 106. The vibrator body 106 is
connected to the reciprocative part 105 by means of a
spring 107. The spring 107 is here embodied as a liquid
spring 107. The rotary part 104 may be connected to any
kind of rotary driving motor (not shown), preferably a
fluid-driven hydraulic motor, optionally via a drive-gear
mechanism. A preferred hydraulic motor arrangement for
driving the seismic source will be described in detail
down below.
In the embodiment of Fig. 1, the rotary part 104 is
driven via a conical meshing wheel 108 to allow an
orthogonal drive axis of the motor relative to the rotary
axis of the rotary part 104. Other drive arrangements,
such as involving for instance linear meshing wheels or
chain or belt transmissions, can be selected depending on
the specific design constraints of an individual case.
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The rotary part 104 is supported by bearings 112,
preferably diamond thrust bearings, which are embedded in
a support piece 136. The bearings 112 and the support
piece 136 will be described in more detail later in this
specification. A central channel 102 is provided in the
rotary part 104, which runs essentially coaxial with the
rotary axis of the rotary part 104. This channel may be
provided in the form of a central bore. The purpose of
this channel will be illustrated below.
A force exerted on the housing 110 toward the
formation 103 results in the vibrator body 106 pushing
against the formation 103, causing the reciprocative part
105 to be pressed against the rotary part 104 via the
liquid spring 107. The rotary part is axially supported
in the housing 110 by the bearings 112.
The conical meshing wheel 108 is coupled to the
rotary part 104 via a spline coupling 113 allowing for
some axial play between the rotary part and the conical
meshing wheel 108. Herewith it is achieved that axial
displacement of the rotary part 104, for instance
resulting from wear on the bearings 112, can be
accomodated without causing the drive mechanism to jam.
The reciprocative part 105 is coupled to the housing
110 of the actuator by means of a spline section 111,
allowing an axial sliding movement of the reciprocative
part 105 relative to the housing 110.
The rotary part 104 and the reciprocative part 105
are provided with conversion means in the form of
corrugated coupling surfaces 109 have profiles that
substantially lie in a plane perpendicular to the axis of
rotation of the rotary part 104. The corrugated coupling
surfaces 109 are slidably arranged with respect to each
other.
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The corrugated coupling surfaces 109 can be provided
on separate crown pieces that are mounted onto the rotary
part 104 and the reciprocative part 105, or they can be
machined directly on these rotary and reciprocative
parts. In order to generate a preferred seismic waveform,
at least one of the coupling surfaces 109 is corrugated
with sinusoidal profile. It is understood that any one of
the coupling surfaces, or both of them, can have a
sinusoidal profile.
The actuator is immersed in a functional fluid,
suitably an oil, for lubrication and/or cooling of the
moving parts, notably including one or more of the
bearing surfaces 112 and the corrugated coupling surfaces
109. The functional fluid is held in a cavity 117 formed
by housing 110 and end piece 118. Pressure balancing
means can be provided to balance the pressure of the
functional fluid (Poil) against the ambient pressure
(Pmud). As an example, a pressure communication channel
119 is provided that connects the cavity 117 with the
ambient, for instance a subterranean borehole, to allow
the pressures Poil and Pmud to assume the same value. A
separator body 116 may be provided inside the pressure
communication channel 119 to avoid intermixing of the oil
and the ambient. The separator body 116 may be a flexible
wall, in the form of piston element slidably arranged in
the cylindrical bore 119 or a membrane wall (not shown).
Fig. 2 shows a detailed view of the bearing support
piece 136 holding a first bearing piece 112A of a pair of
diamond thrust bearings which may comprise
polycrystalline diamond compact (PDC) material. The
support piece 136, which fits with seal 135 in a bore
provided in the housing 110, is formed of material having
a high thermal conductivity, such as brass for example,
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to support cooling of the bearing piece 112A. The second
bearing piece 112B is to be connected to the rotary part
104, preferably also by means of a thermally conducting
support piece 137 (shown in Fig. 1).
Referring to Fig. 2 and Fig. 1, a central hole 134
is provided in the second bearing piece 112B, which is to
be aligned with the central bore 102 in the rotary part
104. One or more grooves 133 are provided in the surface
of the second bearing piece 112B that is to face, and
engage with, the first bearing piece 112A.
When the two bearing pieces are in engagement, the
one or more grooves 133 each form a channel to establish
fluid communication between the central hole 134 and the
ambient of the bearing pieces 112 in the vicinity of
their periphery. As will be further explained below, the
one or more grooves are provided to suck up functional
fluid from the housing cavity 117. Alternatively, the one
or more grooves may be provided in the first bearing
piece 112A instead of, or in addition to, the grooves 133
provided in the second bearing piece 112B.
Referring now to Fig. 1, it can be seen that the
central bore 102 branches into one or more channels 99
each having a radial component with respect to the rotary
axis of the rotary part 104. These channels 99 debouche
in a gap between the rotary part 104 and the
reciprocative part 105, which gap leads to the corrugated
coupling surfaces 109. As will be further explained
below, the one or more channels 99 are provided as
injection means for injecting the functional fluid 117
between the corrugated coupling surfaces 109.
The central channel 102 in the reciprocative part
104 fluidly connects also to a central channel 98
provided in reciprocative part 105. The central channel
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98 branches into one or more channels 97 which debouche
between the splines in spline section 111.
Fig. 3 shows individual views of the rotary part 104
and reciprocative part 105 of the seismic source of Fig.
1. An open end of the central channel 102 in the rotary
part 104 is visible, as well as open ends of the one or
more channels 97 debouching between the splines 111 of
the reciprocative part 105. The coupling surface 109A of
the rotary part 104 has a sinusoidal profile in the
circumferential direction around the rotary axis. The
amplitude of this profile is larger than that of the
circumferential sinusoidal profile of the coupling
surface 109B of the reciprocative part 105. In other
words, the profiles of the coupling surfaces 109 do not
fully match each other. In this way, there always remains
areas with a gap between parts of the coupling surfaces
109, which can hold some of the functional fluid for
lubrication and/or cooling purposes.
The spline section 111 prevents rotation of the
reciprocative part 105 inside the housing 110. Because of
the mechanical interaction of the corrugated coupling
surfaces 109, a rotation of the rotary part 104 is
converted into a reciprocal movement of the reciprocative
part 105.
Still referring to Fig. 3, the rotary part 104 is
provided with a shaft end 140 which is to be slidingly
inserted into a receiving bore 141 that is provided in
the reciprocative part 105. Herewith a proper axial
alignment of the rotary part 104 on the reciprocative
part 105 is ensured whereby the rotary part 104 is
rotatable relative to the reciprocative part 105 while
the latter is axially reciprocable relative to the rotary
part 104.
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The resulting amplitude and oscillatory waveform
imposed on the reciprocative part 105 is determined by
the profiles of the corrugated surfaces 109. An amplitude
lying in a range between 0.01 and 1.0 mm is found
suitable for actuating the seismic waves. Preferably, the
amplitude is larger than 0.05 mm in order to transmit a
high seismic power of more than approximately 1 kWatt.
Preferably, the amplitude is lower than 0.6 mm in order
to ensure that the force required to drive the
reciprocative part 105 is deliverable by the spring
without causing damage to the seismic source.
The spring 107 between the reciprocative part 105
and the vibrator body 106 acts as a cushion. It
accommodates a difference in reciprocative amplitude
between the reciprocative part 105 and the formation 3.
Moreover, the spring 107 provides a biasing force on the
reciprocative part 105 to keep it against the rotary
part 104.
In the embodiment of Fig. 1, the spring 107 is a
liquid spring, comprising a pressure chamber. The
reciprocative part 105 and the vibrator body 106 slidably
reach into the pressure chamber. A bore 114 through the
end piece 118, or any other channel, fluidly connects to
the pressure chamber, for enabling controlled supply and
discharge of a spring liquid to and from the pressure
chamber.
A relative movement of the reciprocative part 105
with respect to the vibrator body 106 causes compression
or decompression of the spring liquid, which results in a
spring stiffness depending on the volume of the pressure
chamber and the compressibility modulus of the spring
liquid. Stiffness is a measure in units of force over
units of length, and is defined as the force required to
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achieve a certain amount of shortening of the spring by
compressing it.
A high-pressure pump (not shown), optionally
separated from the pressure chamber 107 by means of a
check valve (not shown), is connected to the bore 114 for
pressurising the spring liquid inside the chamber 107.
Herewith a base pressure of the spring liquid inside the
pressure chamber 107 can be established, for pre-loading
of the vibrator body 106 against the formation 103 and
bringing the corrugated coupling surfaces 109 into
mechanical engagement with each other and keeping them
into mechanical engagement throughout operation. Bore 114
and the high-pressure pump thus function as adjustment
means for varying the stiffness of the spring 107.
Advantageously, the high pressure pump is driven by
the same motor as the rotary part 104. This way, the
pressure in the liquid spring 107 is increased in concert
with the rotary frequency of the rotary part 104.
The liquid for the liquid spring may be any liquid,
in particular it may comprise one of the group of water,
oil, silicone gel, transducer gel for ultrasonic
echoscopy. Compared to water, oil and silicone gel tend
to have a compressibility of approximately 0.5, whereas
the transducer gel for ultrasonic echoscopy, with a
compressibility of approximately 4, is an example of a
spring liquid having a compressibility higher than that
of water.
In operation, by rotating the rotary part 104, the
reciprocative part 105 will start vibrating in an axial
direction against the spring 107 as a result of the
corrugations in the corrugated coupling surfaces 109.
Spring 107 transmits the reciprocating motion of the
reciprocative part 105 into an oscillatory actuated force
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onto the formation 103. In this way, the internal forces
in the seismic source and the external forces exerted on
the formation 103 can be kept within limits to prevent
damage to the seismic source and the formation 103. Due
to mechanically driving the reciprocative part 105, a
high seismic power can be transmitted.
The seismic source produces a well-defined seismic
waveform of a controlled frequency as long as the
corrugated coupling surfaces 109 remain in contact with
each other. The frequency of the reciprocative motion is
determined by the rotational speed of the rotary part 104
multiplied by the highest number of corrugations on the
coupling surfaces 109. The waveform is determined by the
profiles of the coupling surfaces 109. The amplitude is
independent of the frequency as long as full engagement
of the coupling surfaces 109 is be maintained. This is
achieved by ensuring that the spring 107 is sufficiently
stiff.
Initially, the force exerted on the coupling
surfaces 109 by the spring 107 may preferably be
relatively low so as to facilitate the starting up of
rotational motion of the rotary part 104 against the
friction imposed by the coupling surfaces 109. As the
frequency is increased, however, the oscillatory
acceleration forces required on the reciprocative part
105 to maintain mechanical contact between the corrugated
coupling surfaces 109 also increase. Therefore, it is
preferred to increase the spring liquid pressure in the
liquid spring 107, in response to an increase in the
frequency of the reciprocative part 105. To this end, the
high-pressure pump that provides the pressure in the
spring chamber 107 is preferably coupled to the rotary
part 104 or to the system that drives the rotary part 104
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so that the pressure is concertedly increasable with the
rotation frequency of the rotary part 104.
The function of the central bores 102 and 98 is
illustrated as follows. The rotation of the rotary part
104 relative to the housing 110 drags some of the
functional fluid 117 that is present between the
corrugated coupling surfaces 109 into rotation as well.
As a consequence, that portion of the functional fluid
experiences a centrifugal force, resulting in the
functional fluid being launched out of the area between
the corrugated coupling surfaces 109. This, in turn,
creates an under pressure in the area between the rotary
part 104 and reciprocative part 105 which drives a
circulation of functional fluid from the housing cavity
117, respectively through the one or more grooves 133
provided in the bearings 112, the central channel 102 and
the one or more channels 99 back into the housing cavity
117. The circulation as described, facilitates in cooling
and possibly also in lubrication of the bearings 112 and
the corrugated interaction surfaces. A second circulation
path is formed via the central channel 98 and the one or
more channels 97 in the reciprocative part 105.
Circulation of the functional fluid is driven,
provided that the centrifugal force on the functional
fluid between the corrugated interaction surfaces 109 is
different from the centrifugal force on the functional
fluid in the grooves 133. In the seismic source of Fig.
1, for this reason the corrugated coupling surfaces 109
have a larger peripheral radius than the inlets of the
central bore 102.
The seismic source as described above can be run
into a borehole on a wireline, or integrated in a
drilling assembly.
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Fig. 4 schematically shows an embodiment of the
seismic source integrated into a drill collar 10. In
order to facilitate engagement of the seismic source with
the formation 103, a stabiliser rib 121 or any other kind
of pad can be provided in the vicinity of the seismic
source. In the embodiment of Fig. 4, a separate clamping
piston arrangement 123 is provided which can be
pressurised using a system fluid under a system pressure
Ps, resulting in a radial displacement of the clamping
pistons 123 into engagement with the formation 103.
Optionally, engagement pads 124 can be provided to
distribute the clamping force exerted by the clamping
pistons 123 over a larger area.
A mud passage 122 is present which bypasses the
seismic source. Mud can be fed into the mud passage via
mm÷.
The rotary part 104 of the actuator is driven by a
motor housed in housing 126, which motor in this example
engages via a clutch 127 and drive shaft 128 with a drive
gear 125 based on meshing gear wheels. The clutch is
optionally provided to allow the coupling to slip in case
of a jam. The motor is powered via a pressurised fluid
The liquid spring 107 is pressurised using the
system pressure and a hydraulic piston arrangement 131. A
valve 129 is provided for filling the liquid spring 107
with a suitable liquid, and check valve 130 is provided
to enclose the pressure chamber of the liquid spring 107
against cyclic overpressure induced by the reciprocative
movement of the reciprocative part 105. Seals 115
slidably engage against the vibrator body 106.
In the embodiment of Fig. 4, the rotary axis of the
rotary part 104 and the reciprocative axis 132 both lie
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in an direction orthogonal to the drill string axial
direction.
An attractive alternative arrangement to the one
shown in Fig. 4 is schematically depicted in Fig. 5. The
sliding axis 137 of the vibrator body 106 is arranged
orthogonal to the drill string like is the case in Fig.
4, in order to engage with the formation 103 on the bore
hole wall and transmit seismic p-waves into the formation
transverse to the bore hole. The main difference with the
embodiment of Fig. 4, is that in Fig. 5, the rotary axis
of the rotary part 104 and the reciprocative axis 132 are
arranged parallel to the axial direction of the drilling
assembly which is normally axially arranged in the
borehole. The liquid spring 107 serves to divert the
direction of the force exerted by the reciprocative part
105 on the vibrator body 106.
This principle can be applied in other embodiments
of the seismic source of the invention. It is envisaged
that this embodiment is easier to install in a drill
string, because the actuator is in many practical
embodiments larger in its direction parallel to the
rotary axis and reciprocative axis than it is in the
orthogonal direction.
The seismic source of the invention is capable of
producing between 1 and 5 kWatt of seismic power.
Preferably the seismic power is limited to between 1 and
2 kWatt. The frequency ranges from zero upto 5 kHz, but
in a seismic study the frequency is preferably selected
in a range of between 9 Hz and 2 kHz. The seismic source
is particularly suitable for frequencies higher than
90 Hz, more preferably of higher than 0.9 kHz.
In a specific laboratory test using a seismic
source in accordance with Fig. 1, the reciprocative
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part 105 was preloaded against the rotary part 104 by
approximately 15 kN, using a liquid pressure in the
liquid spring 107 of approximately 80 bar, during
starting up of the rotation until a frequency of
approximately 50 Hz was reached. While further increasing
the frequency to 1.5 kHz, the load on the reciprocative
part 104 was increased to approximately 40 kN by
dynamically increasing the pressure in the liquid
spring to approximately 200 bar. The corrugated
coupling surfaces 109 were provided with a profile
containing 22 sinusoidal corrugations. Thus, to obtain a
frequency of 1.5 kHz, the rotary part 104 was rotating at
some 4000 rpm.
Any suitable drive means may be utilized for driving
the rotary part 104 into rotation. A preferred hydraulic
motor arrangement for driving the seismic source as
described above, is nevertheless shown in Fig. 6 to 10.
Fig. 6 shows a hydraulic motor arrangement
comprising a hydraulic motor 1, which in this case is
a rotary motor, which can be coupled to the rotary
part 104 for driving it into rotation. Other types of
hydraulic motors may be used as well. The hydraulic
motor 1 is drivable by passing a drive liquid under
pressure from inlet channel 2 through the hydraulic
motor 1 to outlet channel 3. The hydraulic motor 1 is
incorporated in an expel system which, in the embodiment
of Fig. 1, includes a bridge manifold 100 for directing
the flow of the drive liquid through the hydraulic
motor 1. Further details of the bridge manifold 100 will
be elucidated later in this specification.
The hydraulic motor arrangement is further provided
with a first expel reservoir 10, and a second expel
reservoir 20. The first expel reservoir 10 is arranged to
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hold the drive liquid that is to be passed through the
hydraulic motor 1. The expel reservoir 10 is for this
purpose fluidly connected to the bridge manifold 100 via
a channel 11. The expel reservoir 10 is further connected
to channel 12, which branches into a working fluid
discharge line 13, and a working fluid supply line 14.
Valve 331 is provided in working fluid discharge line 13,
and valve 341 is provided in the working fluid supply
line 14.
The second expel reservoir 20 is arranged to receive
the drive liquid that has been passed through the
hydraulic motor 1. This expel reservoir 20 is therefore
fluidly connected to the bridge manifold 100 via channel
21. The second expel reservoir 20 is further connected to
channel 22, which branches into a working fluid discharge
line 23, and a working fluid supply line 24. Valve 231 is
provided in working fluid discharge line 23, and valve
241 is provided in the wording fluid supply line 24.
Lines 14 and 24 thus form a supply manifold which
can be fluidly connected to a pressurised working fluid
supply. The valves 341 and 241 make it possible to select
which of the first or second expel reservoirs is exposed
to the pressurised working fluid.
Lines 13 and 23 debouche into a low pressure zone LP
where the fluid pressure is lower than that of the
pressurized working fluid. Valves 331 and 231 determine
which of the expel reservoirs is exposed to the low
pressure zone LP.
The bridge manifold 100 fluidly connects channel 11
to channel 21. Channel 11 branches into a line 54
provided with a check valve 44 in blocking direction, and
into a line 51 provided with a check valve 41 in flow
direction. Following line 51 through the check valve 41,
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the line branches into lines 53 and 55. Line 53 is
provided with check valve 43 in blocking direction. Line
51 connects to line 2 leading to the hydraulic motor 1.
Line 55 is provided with a valve 45 which can be opened
or closed, and choke 46, both in series. Choke 46 is a
variable flow restriction device.
An optional auxiliary line 49 is provided downstream
valve 45 and upstream choke 46. This auxiliary line can
be connected to the seismic source for triggering or
activating the seismic source as a result of pressurising
line 49 prior to driving the hydraulic motor 1. For
instance, the auxiliary line may be connected to
pressurize a clamping piston arrangement 123 such as is
shown in Fig. 4, resulting in a radial displacement of
the clamping pistons 123 into engagement with the
formation 103. Or the auxiliary line may be connected to
pressurize the liquid spring 107 of the seismic source.
Line 3, downstream the hydraulic motor 1, branches
into line 54 on the other side of check valve 44
mentioned above with respect to channel 11, and into line
52 which is also provided with a check valve 42. Both
check valves 44 and 42 are in flow direction. However,
due to the pressure loss in the hydraulic motor 1, there
will be a pressure differential across check valve 44
preventing flow through that check valve. Flow through
line 52 is possible, and downstream check valve 42 the
line branches into lines 53 and 21. Line 53 is provided
with a check valve 43 in flow direction, but since
downstream check valve 43 line 53 is in fluid
communication with line 51 which is upstream the
hydraulic motor 1, the pressure differential across check
valve 43 will prevent passage.
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To prevent the hydraulic motor 1 from being damaged
by its own inertia, a safety valve 47 can be applied as
shown in Fig. 6, in a bypass line 48 shorting the
hydraulic motor 1 by connecting the inlet line 2 and
outlet line 3. The safety valve can be a check valve,
blocking flow from line 2 to line 3 and allowing flow
from line 3 to line 2. Herewith it is achieved that, in
case hydraulic motor 1 is in motion while the pressure
differential across the hydraulic motor 1 is not
sufficient to drive it, the hydraulic motor 1 can
drive circulation of the drive liquid through the bypass
line 48.
The function of the bridge manifold 100, is to
ensure that the drive liquid always flows in the
direction of arrow 4 through line 55, no matter which one
of the expel reservoirs 10 or 20 is pressurised.
In a preferred embodiment, the hydraulic motor
arrangement is suitable .for being suspended in a
subterranean bore hole and/or for being contained in a
drill string. As an example, the hydraulic motor
arrangement of Fig. 6 is installed in a drill string 5
reaching into a subterranean borehole 6 containing
drilling mud, as schematically depicted in Fig. 7. The
drilling mud can be circulated in a conventional way,
wherein the drilling mud is pumped at the surface into a
conduit 7 formed by the drill string 5, released into the
borehole via an opening near the bottom end 8 of the
drill string, and led back to the surface via an annular
space 9 between the borehole wall and the drill string 5.
Lines 14 and 24 (Fig. 6) are fluidly connected, via
valves 341 and 241, to the drilling mud inside the drill
string conduit 7, whereas lines 13 and 23 (Fig. 6) are
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fluidly connected, via valves 331 and 231, to the annular
space 9.
In operation, the hydraulic motor arrangement of
Fig. 6 works as follows. In an initial condition, expel
reservoir 10 holds a good amount of drive liquid, and
expel reservoir 20 holds an approximately similar amount
of drilling mud. Valves 331, 341, 231, 241, 45, and choke
46 are closed. Drilling mud is circulated as described
above, resulting in a pressure differential between the
drilling mud pressure inside drill string conduit 7 and
the drilling mud pressure in the annular space 9. Thus,
the drill string conduit 7 is the high-pressure side HP
of the hydraulic motor arrangement, and the annular space
9 is the low-pressure side LP.
Valve 341 is opened, thereby fluidly connecting
expel reservoir 10 to the drill string conduit 7. Opening
valve 341 will expose the drive liquid in reservoir 17 to
the inner drill string pressure at no flow. Then valve
231 is opened, thereby connecting expel reservoir 20 to
the annular space 9. Opening valve 231 will enforce the
annulus pressure at no flow.
Opening valve 45 will deliver pressure to optional
auxiliary line 49, at limited flow to trigger or activate
the optional auxiliary apparatus, prior to driving the
hydraulic motor 1. Gradually opening choke 46 will
create an increasing flow of drive liquid from expel
reservoir 10 to expel reservoir 20 (via lines 11, 51, 55,
2, 3, 52, and 21 respectively, as explained above), until
the driving fluid has been displaced and expelled from
the expel reservoir 10 by the pressurised drilling mud
entering the expel reservoir 10 as the working fluid, and
until the drilling mud has been displaced and expelled
from the expel reservoir 20 by the drive liquid entering
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the expel reservoir 20. Controlling the choke 46 thus
controls the operation of the hydraulic motor.
By closing all the valves, and opening valves 241
and 331 instead of 341 and 231, the hydraulic motor
arrangement can be operated again, whereby drilling mud
is received by expel reservoir 20, thereby displacing and
expelling the drive liquid via respective lines 21, 53,
55, 2, 3, 54, and 11 into expel reservoir 10 again.
This cycle can be repeated.
Fig. 8 shows an alternative hydraulic motor
arrangement, having an expel system with a simpler
manifold 101 than the bridge manifold 100 of Fig. 6.
Manifold 101 is based on one check valve 40.
Like Fig. 6, the hydraulic motor arrangement of
Fig. 8 is provided with first and second expel reservoirs
10 and 20, connected to manifold 101 via lines 11 and 21,
respectively. Like in the embodiment of Fig. 5, the
second expel reservoir 20 is arranged to receive the
expelled drive liquid and, upon receipt thereof, to
displace and expel working fluid into the low pressure
zone so that the drive liquid can be collected in the
second expel reservoir 20, and recirculated through the
hydraulic motor arrangement for use in a next cycle.
The manifold 101 comprises line 50 which fluidly
connects line 11 with line 12. Line 50 is separated from
line 11 by means of valve 45. Check valve 40 is located
in line 50 allowing flow in the direction from second
expel reservoir 20 to first expel reservoir 10, and
blocking flow in the reverse direction. The hydraulic
motor 1 is located in line 60 which is arranged to bypass
the check valve 40. Line 60 is also provided with a
variable flow restriction device in the form of choke 46.
Optionally, line 60 may be provided with a check valve
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for blocking the flow path from the second expel
reservoir 20 to the first expel reservoir 10 through
line 60.
Similar to the embodiment of Fig. 6, manifold 101
may be provided with optional auxiliary line 49, which in
the embodiment of Fig. 8 may connect to line 50 between
valve 45 and check valve 40. A bypass line 48, shorting
the hydraulic motor 1, including a safety valve 47 can be
provided to protect the hydraulic motor 1 in the same way
as is shown in Fig. 6.
The expel reservoirs 10, 20, and the supply
manifolds and low pressure zones LP can be the same as,
or similar to, the ones of Fig. 6. The function of
manifold 101, is to ensure that the drive liquid always
flows in the direction of arrow 4 through line 60.
The hydraulic motor arrangement of Fig. 7 works as
follows. In an initial condition, expel reservoir 10
holds a good amount of drive liquid, and expel
reservoir 20 holds an approximately similar amount of
working fluid, which can be a drilling mud. Valves 331,
341, 231, 241, 45, and choke 46 are initially closed. A
pressure differential is established between the HP and
the LP zones, for instance in the way described above
involving circulation of drilling mud. Valve 341 is
opened, thereby fluidly connecting expel reservoir 10 to
the working fluid in the high pressure zone HP. Opening
valve 341 will expose the drive liquid in reservoir 17 to
the pressurised working fluid at no flow. Then valve 231
is opened, thereby connecting expel reservoir 20 to the
low pressure zone LP. There is still no flow of the drive
liquid.
Opening valve 45 will deliver pressure to optional
auxiliary line 49, at limited flow to trigger or activate
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an optional auxiliary apparatus, prior to driving the
hydraulic motor 1. Gradually opening choke 46 will create
an increasing flow of drive liquid from expel reservoir
to expel reservoir 20 (via lines 11, 50, 60, 50, and
5 21 respectively), until the driving fluid has been
displaced and expelled from the expel reservoir 10 by
the pressurised working fluid entering the expel
reservoir 10, and until the exhaust fluid has been
displaced and expelled from the expel reservoir 20 by the
10 drive liquid entering the expel reservoir 20. Controlling
the choke 46 controls the operation of the hydraulic
motor.
By closing all the valves, and opening valves 241
and 331 instead of 341 and 231, the hydraulic motor
arrangement is reset to its initial condition, after
which the cycle can be repeated. Since choke 46 and
hydraulic motor 1 impose a flow resistance in line 60,
the drive liquid will flow through check valve 40 from
expel reservoir 20 back to expel reservoir 10 provided
that valve 45 is opened.
The general principle of the hydraulic motor
arrangements included in a drill string for instance such
as is shown in Fig. 7, is that it is driven by virtue of
the pressure differential between the drill string
conduit 7 and the annular space 9. Alternatively, a
pressure differential can be created within the drill
string conduit 7 by provision of a suitable flow
restriction, whereby lines 14 and 24 should connect to
the drill string conduit 7 upstream of the flow
restriction and lines 13 and 23 should connect to the
drill string conduit 7 downstream of the flow
restriction.
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It will be understood that the hydraulic motor
arrangement described with reference to Fig. 8 can be
installed in a drill string in the same way as shown in
Fig. 7. An advantage of the hydraulic motor arrangements
described above, is that the drive liquid can be fully
optimised for driving the hydraulic motor 1, and the
drilling mud can be fully optimised for its purpose as a
drilling fluid. Delicate mechanisms such as the choke 46
and the drive mechanism in hydraulic motor 1 are not
exposed to the harsh conditions imposed by passing
drilling mud.
In the described hydraulic motor arrangement the
pressure of the pressurized working fluid is transferred
to the drive liquid in the expel reservoir, and then
utilized for driving the hydraulic motor. The drive
liquid can thus be optimised for its task of driving the
hydraulic motor independently from specific requirements
of the working fluid. For instance, a clean hydraulic oil
that is free of erosive solid particulates can be
utilised, which would be unsuitable as a drilling mud but
particularly suitable for driving a hydraulic motor.
Another advantage of the hydraulic motor arrangement
in accordance with the invention is that it can be
operated using a gaseous working fluid even when the
hydraulic motor requires a liquid driving fluid.
In order to prevent the drive liquid from being
contaminated by the working fluid, a movable wall 15,25
is provided in the expel reservoirs 10,20 separating two
compartments 16,17 and 26,27 in each of the expel
reservoirs 10,20. First compartments 16 and 26 are
reserved for receiving and containing the working fluid,
and second compartments 17,27 are reserved for receiving
and containing the drive liquid. The movable wall 15,25
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may be provided in the form of a piston means which is
slidably arranged in a cylindrical bore which is in fluid
communication with the first and second compartments in
the expel reservoir concerned.
Alternatively, the movable wall 15,25 may be
provided in the form of a flexible membrane, such as a
rubber membrane.
In order to avoid the inlets to the compartments to
be blocked by the movable wall, as a result of the wall
being forced into the compartment by the load in the
compartment, one or both of the compartments may be
provided with a porous section to ensure that the inlets
are in communication with a good deal of the volume
inside the compartments. Such a porous section can for
instance be provided in the form of inwardly protruding
ribs on the inside walls of the compartments, or in the
form of a flexible sponge-like material.
In the preferred embodiments, there is a
predetermined fixed amount of drive liquid present in the
expel system. In order to avoid the blockage problem in
the working fluid compartment, it is possible to provide
excess volume in the working fluid compartment such that
an amount of the working fluid remains present in the
expel reservoir in the situation that a maximum amount of
drive liquid is present in the expel reservoir.
The hydraulic motor arrangements as depicted in
Figs. 6 and 8 are suitable for intermittently operating
the hydraulic motor 1 during limited periods of time of
which the maximum duration is dictated by the volume that
is available in the expel reservoirs for exchanging drive
liquid. The hydraulic motor arrangements are also
particularly suitable for imposing a frequency sweep on
the hydraulic motor 1, by gradually opening choke 46.
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A quasi-continuous operation of the hydraulic motor
1 is achievable in the embodiment of Fig. 6 by
appropriate concerted switching of valves 331, 231, 341,
and 241, provided that the hydraulic motor 1 contains
sufficient inertia to bridge the switching time.
For a more continuous operation, the hydraulic motor
arrangement of Fig. 6 can be modified by providing at
least three, and preferably at least four expel
reservoirs in a "cyclic star"-arrangement whereby the
expel reservoirs for instance go through their cycles
with fixed phase differences.
The cycle can be operated again and again, and in
this way a continuous flow of driving liquid through the
hydraulic motor can be maintained.
Fig. 9 schematically shows a preferred embodiment of
a hydraulic motor arrangement as a drill string sub,
which can be a section of a drill string. The first and
second expel reservoirs 10,20 are disposed upstream and
downstream of a unit 300 comprising a hydraulic motor.
The expel reservoirs are shaped as a torus around a
centrally disposed drilling mud passage 71. Cylindrical
membranes 15,25 separate the respective compartments
16,26 for working fluid such as drilling mud, from
compartments 17,27 for drive liquid such as hydraulic
oil. In this example the outer compartments 16,26 are
assigned as the working fluid compartments and the inner
compartments 17,27 as the drive liquid compartments, but
this may be assigned the other way round if so desired.
Compartments 201 to 204 are provided for housing the
necessary valve means, and optionally other means such as
control electronics and batteries for powering the
control electronics and optionally also for powering the
valves.
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Fig. 10 shows a detailed embodiment for the torus
shaped expel reservoir 10. This embodiment is also
applicable for the expel reservoir 20. In this
embodiment, the expel reservoir is arranged inside an
outer tube 79, which is sandwiched between a cover body
75 on a mud side and a cover body 85 on a drive liquid
side. Cover body 75 is provided with a supply/discharge
channel 76 for supplying and discharging working fluid in
the form of a drilling mud, and cover body 85 is provided
with a supply/discharge channel 86 for supplying and
discharging drive liquid. Supply/discharge channels 76
and 86 respectively correspond to lines 12 and 22 as
schematically depicted in Figs. 6 and 8.
Connected to the respective cover bodies 75 and 85
are membrane liners 72 and 82, which are connected by
means of fastening means 77 and 87. The cover bodies 75,
85, and the membrane liners 72, 82, are provided with a
central bore, which fluidly connects to a central tube 74
to form the centrally disposed drilling mud passage 71
which bypasses the expel reservoirs.
Membrane 15 is clamped between the membrane liners
72, 82 and respective clamping rings 73 and 83 which are
connected to their membrane liners 72, 82 by fastening
means 78 and 88 such that membrane 15 is held between the
membrane liners 72, 82 and the respective clamping rings
73, 83. The membrane liners 72, 82 and/or the clamping
rings 73, 83 are preferably provided with corrugated
clamping surfaces to axially secure the membrane 15.
A working fluid compartment 16 is formed by the
annular space defined between the outer tube 79 and the
membrane 15, and a drive liquid compartment 17 is formed
by the annular space defined between the inner tube 74
and the membrane 15. The clamping ring 73 on the mud side
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is provided with a channel 70 that fluidly connects the
working fluid compartment 16 with supply/discharge
channel 76. Channel 70 can be provided in the form of a
bore, but in the embodiment of Fig. 10 it is provided in
the form of a groove in the outer periphery of the
clamping ring 73 which groove together with the outer
tube 79 forms the channel 70.
In a similar way, the membrane liner 85 on the
working fluid side is provided with a channel 80 that
fluidly connects the drive liquid compartment 17 with
supply/discharge channel 86.
The outside wall of the inner tube 74 is provided
with annular grooves to avoid the membrane 15 to fully
engage with the inner tube and thereby block the channel
80. There is an excess volume reserved in the working
fluid compartment 16 as compared to the volume of drive
liquid that can be brought into the drive liquid
compartment 17 under normal operation, in order to avoid
the channel 70 from being blocked by the membrane 15.
Referring to Figs. 9 and 10, in a practical example,
the outer diameter D1 of the stabiliser pads 121 on
drill pipe section can be 215 mm suitable for a
so-called 8%"-hole. The diameter D2 of the drilling
fluid passage 71 can be 38 mm (corresponding to 1%") and
the outer diameter D3 of the outer tube 79 can be 170 mm
(corresponding to 6k"). Assuming an axial length Ll of 1
meter, there is space available for approximately 10
litres of drive liquid to exchange between the expel
reservoirs 10 and 20. Further assuming a pressure
differential of 80 bars between the working fluid supply
point and the working fluid discharge point, which is
realistic for drilling mud in a subterranean drilling
operation, and a flow of 1 litre/second, this hydraulic
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motor arrangement should be able to deliver 7.8 kWatt for
a duration of 10 seconds. Useful seismic data should be
obtainable during this amount of time.
